In most communications system the antenna is a very important part of the design. In MMW communications systems, the antenna may be very small due to the short wavelength. For such a small size antenna, high radiation efficiency and high coupling efficiency may be important considerations.
A MMW antenna is often made on a printed circuit board (PCB) or other solid substrate. Prior art PCB substrates may have a high loss factor for MMW and hence the radiation efficiency of an antenna built on this kind of substrate may be less than optimal.
One possible improvement is to use special processing on low loss material such as MicroElectroMechanical Systems (MEMS) processing on glass (alumina). However this may involve complex processing and high cost.
The coupler from the IC die to the substrate where the antenna is, may also cause loss. Although the antenna may be located on the IC die (on-chip antenna) to avoid some coupling loss and reduce the size, the radiation efficiency of an on-chip antenna may very low due to the high loss tangent of the IC die.
Another approach is using a bond wire on the signal port on the IC die and design the wire's length and shape so that the bond-wire works as an antenna. Because the bond wire is over air, the loss of the IC die and PCB substrate has little effect to the antenna. Such an antenna is called bond-wire antenna (BWA).